Research Product

Colonization of glass substrata by populations of three or four bacterial species over periods of four weeks or more was investigated using recirculating, model laboratory systems. Numbers of a coryneform, Aeromonas hydrophila, Pseudomonas fluorescens, and Xanthomonas maltophilia on surfaces and in the liquid phase were monitored to determine whether any species inhibited or facilitated the colonization by another organism. The system was 800 ml of culture in a peptone/yeast extract/artificial lakewater medium, pulse-fed every three days, and recirculated at 12 ml min-1. Species numbers were determined by viable counts on differential media, and biofilm coverage was evaluated by computer-enhanced microscopy. The coryneform quickly colonized the surfaces, and there was little change in suspended or attached numbers over the experimental period. Colonization by A. hydrophila increased in the presence of P. fluorescens. X. maltophilia was a highly adhesive strain and promoted microcolony formation on the surface. The influence of nutrient concentration on colonization was determined by testing media at 10-1, 10-2, and 10 to the first power dilutions of the standard concentrations. The relative proportions of species both in the liquid and on surfaces altered with different nutrient concentrations. A. hydrophila was the least efficient colonizer, particularly at the two lowest dilutions, and its colonization increased when P. fluorescens was present. With increase in nutrient concentration, there was a greater increase in total numbers of bacteria in the liquid (ranging from 7.7 x 10 to the sixth power ml-1 to 1.7 x 10 to the tenth power ml-1) than on the surfaces (ranging from 6.3 x 10 to the third power cm-2). The results indicated that the ability of bacteria to colonize surfaces is to a large extent related to their ability to colonize the liquid phase. However, when a species has strong adhesive characteristics, this can result in relatively greater colonization of surfaces. In addition, synergistic interspecies interactions may allow a poor colonizer to become established.